U.S. patent number 6,296,691 [Application Number 09/433,243] was granted by the patent office on 2001-10-02 for multi-functional molded filter for removing contaminants from an enclosure.
This patent grant is currently assigned to Gore Enterprise Holdings, Inc.. Invention is credited to Rajan Gidumal.
United States Patent |
6,296,691 |
Gidumal |
October 2, 2001 |
Multi-functional molded filter for removing contaminants from an
enclosure
Abstract
The present invention is an improved molded filter which
performs multiple filtration functions within an enclosed
environment, such as within a computer hard disk drive. In a first
embodiment, the filter is capable of removing particulate
contaminants from both incoming (external) air and recirculating
air by performing both breather and recirculation functions when
placed over a breather hole in a disk drive. In an alternative
embodiment, the filter also incorporates an adsorbent material
which allows it to remove both particulate and vapor phase
contaminants from incoming (external) air and recirculating air
within the disk drive.
Inventors: |
Gidumal; Rajan (Newark,
DE) |
Assignee: |
Gore Enterprise Holdings, Inc.
(Newark, DE)
|
Family
ID: |
26852192 |
Appl.
No.: |
09/433,243 |
Filed: |
November 4, 1999 |
Current U.S.
Class: |
96/17; 360/99.16;
55/385.6; 55/486; 55/DIG.39; 55/DIG.5; 96/135; 96/154; 96/68;
G9B/33.048 |
Current CPC
Class: |
B01D
46/0032 (20130101); B01D 46/0036 (20130101); B01D
46/12 (20130101); B01D 53/02 (20130101); G11B
33/1486 (20130101); B01D 2271/02 (20130101); B01D
2275/10 (20130101); B01D 2279/45 (20130101); G11B
25/043 (20130101); Y10S 55/05 (20130101); Y10S
55/39 (20130101) |
Current International
Class: |
B01D
46/10 (20060101); B01D 46/12 (20060101); B01D
53/02 (20060101); G11B 33/14 (20060101); G11B
25/04 (20060101); B03C 003/30 () |
Field of
Search: |
;96/17,68,69,135,139,147,153,154 ;55/385.6,486,DIG.39,DIG.5,DIG.12
;264/DIG.48 ;360/97.02 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
19814514 |
|
Dec 1998 |
|
DE |
|
WO 97/00717 |
|
Jan 1997 |
|
WO |
|
Other References
International Search Report for PCT/US00/25806 (2 pages), Dec. 29,
2000..
|
Primary Examiner: Chiesa; Richard L.
Attorney, Agent or Firm: Lewis White; Carol A.
Parent Case Text
RELATED APPLICATIONS
The present application is a regular application based on
co-pending United States Provisional Patent Application No.
60/155,290 filed Sept. 21, 1999.
Claims
I claim:
1. A filter adapted for filtering particulates present within and
particulates entering through a breather hole in an enclosed
environment housing sensitive equipment, comprising:
a layered construction comprising at least one protective support
layer, at least one first filter layer selected from the group
consisting of an electret material and a triboelectret material,
and at least one second filter layer, said construction being
molded so that it has a permanent three-dimensional shape defining
a cavity therein;
at least one substantially planar filter layer adjacent said
cavity; and
a perimeter seal sealing the layered construction to the at least
one substantially planar filter layer,
whereby when the filter is located within the enclosed environment
and positioned over the breather hole, the filter is capable of
filtering particulates entering and within the enclosed
environment.
2. The filter of claim 1, wherein said at least one second filter
layer comprises expanded polytetrafluoroethylene membrane.
3. The filter of claim 1, wherein said substantially planar filter
layer comprises expanded polytetrafluoroethylene membrane.
4. The filter of claim 1, wherein said filter further comprises an
adsorbent material within said cavity, and said filter is capable
of filtering gaseous contaminants entering and within the enclosed
environment.
5. The filter of claim 1, wherein said filter further comprises a
diffusion tube adjacent said substantially planar filter layer.
6. The filter layer of claim 5, further comprising an adhesive
layer on at least a portion of said diffusion tube for adhering
said filter to said enclosed environment.
7. The filter of claim 4, wherein the adsorbent material comprises
a material selected from the group consisting of silica gel,
activated carbon, activated alumina, molecular sieves, clays and
superabsorbent fibers.
8. The filter of claim 4, wherein the adsorbent material comprises
a material selected from the group consisting of calcium carbonate,
calcium sulfate, potassium permanganate, sodium carbonate,
potassium carbonate, sodium phosphate and activated metals.
9. The filter of claim 4, wherein the adsorbent material is a
polymeric scaffold that is impregnated with an adsorbent.
10. The filter of claim 9, wherein the polymeric scaffold is
selected from the group consisting of membranes of polypropylene,
polyethylene, polyvinylidene fluoride, polyvinyl alcohol and
polyethylene terepthalate.
11. The filter of claim 9, wherein the scaffold is expanded
polytetrafluoroethylene.
12. The filter of claim 1, wherein said at least one protective
layer is selected from the group consisting of a scrim, a woven and
a nonwoven material.
13. The filter of claim 1, wherein the at least one second filter
layer is selected from polypropylene, nylon, a composite of
polycarbonate and polyester, mixed cellulose ester, polyvinyl
chloride and cellulose triacetate.
14. The filter of claim 1, wherein the at least one substantially
planar filter layer is selected from polypropylene, nylon, a
composite of polycarbonate and polyester, mixed cellulose ester,
polyvinyl chloride and cellulose triacetate.
15. The filter of claim 1, further comprising an adhesive layer on
at least a portion of said substantially planar filter layer for
adhering said filter to said enclosed environment.
16. The filter of claim 1, wherein said filter further includes a
gasket for sealing said enclosed environment.
17. The filter of claim 1, wherein said filter further includes a
damping material for reducing vibration within the enclosed
environment.
18. The filter of claim 1, wherein said first filter layer
comprises a triboelectret material comprising clean porous
polypropylene fibers and clean modified acrylic fibers.
19. A filter adapted for filtering particulates present within and
particulates entering through a breather hole in an enclosed
environment housing sensitive equipment, comprising:
a layered construction comprising at least one protective support
layer comprising a polypropylene scrim material, at least one first
filter layer comprising a triboelectret material comprising clean
porous polypropylene fibers and clean modified acrylic fibers, and
at least one second filter layer comprising expanded
polytetrafluoroethylene membrane, said construction being molded so
that it has a permanent three-dimensional shape defining a cavity
therein;
an adsorbent material within said cavity;
at least one substantially planar filter layer comprising expanded
polytetrafluoroethylene membrane adjacent said cavity;
a perimeter seal sealing the layered construction to the at least
one substantially planar filter layer; and
a diffusion tube adjacent said substantially planar filter
layer,
whereby when the filter is located within the enclosed environment
and positioned over the breather hole, the filter is capable of
filtering particulates entering and within the enclosed
environment.
Description
FIELD OF THE INVENTION
This invention relates to a device for filtering contaminants, such
as particulates and vapor phase contaminants, from a confined or
enclosed environment such as electronic or optical devices
susceptible to contamination (e.g. computer disk drives) by
incorporating multiple filtration functions into a single
filter.
BACKGROUND OF THE INVENTION
Many enclosures that contain sensitive instrumentation must
maintain very clean environments in order to operate properly.
Examples include the following: enclosures with sensitive optical
surfaces, or electronic connections that are sensitive to
particulates and gaseous contaminants which can interfere with
mechanical, optical, or electrical operation; data recording
devices, such as computer hard disk drives that are sensitive to
particles, organic vapors, and corrosive vapors; enclosures for
processing, transport or storage of thin films and semiconductor
wafers; and electronic control boxes such as those used in
automobiles and industrial applications that can be sensitive to
particles, moisture buildup, and corrosion, as well as
contamination from fluids and vapors. Contamination in such
enclosures originates from both inside and outside the enclosures.
For example, in computer hard drives, damage may result from
external contaminants as well as from particles and outgassing
generated from internal sources. The terms "hard drives" or "hard
disk drives" or "disk drives" or "drives" will be used herein for
convenience and are understood to include any of the enclosures
mentioned above.
One serious contamination-related failure mechanism in computer
disk drives is static friction or "stiction". Stiction results from
the increased adhesion of a drive head to a disk while the disk is
stationary plus increased viscous drag parallel to the head-disk
interface. Newer high density disks are more sensitive to
contamination-caused stiction because they are smoother and only
thin layers of lubricants are present. Contaminants on the disk
change the surface energy and the adhesive forces between the head
and disk, which cause stiction. Also, vapors that condense in the
gap between the head and disk can cause stiction. Further
exacerbating these effects are the newer lower energy, lower torque
motors being used in smaller disk drives for portable
computers.
Another serious contamination-related failure mechanism in computer
disk drives is head crashes. Head crashes can occur when particles
get into the head disk interface. Newer high density drives have 30
nanometer or less flying heights or spacing between the head and
disk during operation and typically have disks rotating 5400
revolutions per minute or greater. Even submicron-sized particles
can be a problem, causing the head to crash into the particle or
the disk after flying over a particle, bringing the drive to an
abrupt failure mode. Particles can also adversely affect data
integrity and mechanical reliability of a drive, sometimes referred
to as thermal asperity.
In addition, disk drives must be protected against a large number
of contaminants in the surrounding environment that can penetrate
the drive. This is true for drives used in small to medium sized
computer systems which may not be used in the typical data
processing environment and is especially true in drives that are
removable and portable to any environment such as disk drives that
are used in laptop computers or in Personal Computer Memory Card
International Association (PCMCIA) slots.
Filtration devices to keep particles from entering these enclosures
are well known. They may consist of a filtration media held in
place by a housing of polycarbonate, acrylonitrile butadiene
styrene (ABS), or some other material; or they may consist of a
filtration media in the form of a self-adhesive disk utilizing a
layer or layers of pressure sensitive adhesive. These devices are
mounted and sealed over a vent hole in the enclosure to filter
particulates from the air entering the drive. Filtration
performance depends not only on the filter having a high filtration
efficiency but also on having a low resistance to air flow so that
unfiltered air does not leak into the enclosure through a gasket or
seam instead of entering through the filter. Such filters work well
for particulates of external origin, but do not address the
problems from vapor phase contaminants.
Combination sorbent breather filters to keep particulates and
vapors from entering enclosures are also well known. These can be
made by filling a cartridge of polycarbonate, ABS, or similar
material with sorbent and securing filter media on both ends of the
cartridge. Examples of such filters are described in U.S. Pat. No.
4,863,499 issued to Osendorf (an anti-diffusion chemical breather
assembly for disk drives with filter media having a layer
impregnated with activated charcoal granules); U.S. Pat. No.
5,030,260 issued to Beck et al. (a disk drive breather filter
including an assembly with an extended diffusion path; U.S. Pat.
No. 5,124,856 issued to Brown et al. (a unitary filter medium with
impregnated activated carbon filters to protect against organic and
corrosive pollutants); and U.S. Pat. No. 5,447,695 issued to Brown
et al. (Chemical Breather Filter Assembly). Unfortunately, many of
these designs are too large and take up too much space in today's
miniaturized drives. They again filter only incoming air of
particles and mainly incoming air of vaporous contaminants,
although some internal air can also be cleaned from internally
generated vaporous contaminants since the filters are inside the
drive and these contaminants will diffuse into the adsorbent
sections of the filters. None of these filters address cleaning the
air of internal particles.
A second combination adsorbent breather filter is also well known
that encapsulates the adsorbent material such as an impregnated
activated carbon polytetrafluoroethylene (PTFE) composite layer
between two layers of filter media and is applied over a hole in
the enclosure with a layer of pressure sensitive adhesive. These
filters work well and are of a size that can be used in today's
small drives but are typically designed to filter air coming into
the drive. Thus, the adsorbent is typically primarily desired to
adsorb both organic and corrosive vapors from the outside
environment and will filter particulates only from air coming into
or leaving the drive. Internally generated vapors can be adsorbed
by these filters, but often times they are used in conjunction with
another internal adsorbent so they can be smaller in size;
therefore, such filters do not contain enough adsorbent to
adequately adsorb all the internally generated contaminants. Again,
particles are also generated inside the drive and are not typically
captured by these filters.
A diffusion tube can be included with either the initial
particulate breather filter or an adsorbent breather filter as
described in U.S. Pat. No. 5,417,743 by Dauber. Diffusion tubes
provide additional protection against vaporous contaminants
(including moisture) entering the drive through the breather
opening by providing a diffusion barrier in the form of the
diffusion tube which creates a tortuous or a longer path for air to
travel before entering the drive enclosure. Diffusion tubes reduce
the number of contaminants reaching the interior of the enclosure
(and/or the adsorbent depending on the location of the filter) and
increase the humidity time constants or time required to reach
humidity equilibrium with the environment. As used herein, for
convenience, the term "diffusion tube" may refer to either a
conventional tortuous path or it may refer to a non-tortuous cavity
into which incoming air passes before entering the filter.
Internal particulate filters, or recirculation filters, are also
well known. These filters are typically pieces of filter media,
such as expanded PTFE membrane laminated to a polyester nonwoven
backing material, or "pillow-shaped" filters containing electret
(i.e., electrostatic) filter media. They are pressure fit into
slots or "C" channels and are placed in the active air stream such
as near the rotating disks in a computer hard disk drive or in
front of a fan in electronic control cabinets, etc. Alternatively,
the recirculation filter media can be framed in a plastic frame.
These filters work well for particulate removal of internally
generated particles, but do not address the problem of vapor phase
contaminants, nor do they provide ultimate protection from external
particles entering the drive.
Internal adsorbent filters are also well known. One example is
described in U.S. Pat. No. 4,830,643 issued to Sassa et al. This
patent teaches a sorbent filter where a powdered, granular or
beaded sorbent or sorbent mixture is encapsulated in an outer
expanded PTFE tube. This filter is manufactured by W. L. Gore &
Associates, Inc., Elkton, Md., and is commercially available under
the trademark GORE-SORBER.RTM. module. While this filter is highly
effective at collecting vapor phase contaminants, it is currently
only available in large and medium sizes like filter volumes down
to about 3 cc. In its present form, this filter is incapable of
fully addressing the growing needs for even smaller and more
compact sorbent filters, nor is it designed to filter the internal
air of particulate contamination. A second well known internal
adsorbent assembly incorporates a layer of adsorbent, such as
activated carbon/PTFE composite, between an encapsulating filter
layer and layer of pressure sensitive adhesive that helps
encapsulate the adsorbent as well as provides a means of mounting
the adsorbent assembly on an interior wall in the enclosure. Such a
filter is described in U.S. Pat. No. 5,593,482 issued to Dauber et
al. Again neither of these filters address particulate
contaminants. A third internal adsorbent assembly incorporates a
layer of adsorbent such as activated carbon/PTFE composite between
two layers of filter media or is alternately wrapped in a layer of
filter media and can be installed between slots or "C" channels
much the way a recirculation filter is installed but without much
air flow through the filter. Such a filter is described in U.S.
Pat. No. 5,500,038 issued to Dauber et al., and, as with the other
filters mentioned, this construction does not provide significant
particle capturing capability.
As stated above, all of these internal adsorbent filters work well
at adsorbing vapor phase contaminants, but they do not filter
particulates very well. They can collect particles by some
impaction of particles onto the filter (i.e., by having the larger
particles impacting or colliding with the adsorbent filter as
particle-laden air speeds around the filters) or by diffusion of
particles onto the filter. However, these filters do not perform
nearly as well as standard recirculation filters that work by a
combination of sieving (mechanically capturing particles too large
to pass through the pore structure of the filter), impaction
(capturing particles too large to follow the bending air streams
around filters or the fibers of the filter), interception
(capturing particles that tend to follow the air streams, but are
large enough to still intercept a filter fiber or, in other words,
those particles with a diameter equal to or less than the distance
between the fiber and the air stream line), and diffusion
(capturing smaller particles buffeted about by air molecules in a
random pattern and coming into contact with a filter fiber to
become collected).
A commercially available adsorbent recirculation filter, available
from the Donaldson Company, Inc. incorporates activated carbon
beads glued to a nonwoven carrier that is sandwiched between two
layers of electret filter material and two layers of plastic
support screen. This filter provides some sorbent protection at the
sacrifice of some internal particle filtration effectiveness, as
this construction appears to increase resistance to air flow to the
filter relative to a conventional recirculation filter. The sorbent
capability is limited, however, due to, for example, the
constraints of the filter size and the blockage of sorbent surface
area by the glue holding the carbon to the carrier. Moreover, this
filter does not filter particles from air entering the drive.
Another issue in today's drives is contamination due to corrosive
ions such as chlorine and sulfur dioxide. To adsorb these compounds
the adsorbent is typically treated with a salt to chemisorb the
contaminants. When the filters described in the preceding paragraph
were washed in deionized water, large amounts of these salts were
released, making it unacceptable to today's sensitive disk drive
environments. An alternative washable adsorbent recirculation
filter is described in U.S. Pat. No. 5,538,545 issued to Dauber et
al., wherein expanded PTFE membranes or other hydrophobic materials
are used to encapsulate the adsorbent. However, these filters still
do not filter air as it comes into the drive before it has had a
chance to deposit particles and do damage to the drive.
Combinations of several filters having different functions in a
single drive have been taught. For example, U.S. Pat. No.
5,406,431, to Beecroft, describes a filter system for a disk drive
that includes an adsorbent breather and recirculation filter in
specifically identified locations within the drive. Also, U.S. Pat.
No. 4,633,349, by Beck et al., teaches a disk drive filter assembly
comprising a dual media drum type filter element in a recirculating
filter assembly that surrounds a breather filter. Further, U.S.
Pat. No 4,857,087, to Bolton et al., teaches incorporating a
breather filter in a recirculation filter housing, but has
significantly more parts and incorporates a third filter element
complete with housings, aperatures, and gaskets to accomplish this
inclusion. The combinations described in these patents either
locate the filter components in separate regions of the disk drive
or incorporate space-consuming fixtures to orient the component
parts within the drives.
As disk drives have become smaller and the prices have declined,
there has been a push for simplification and the reduction in the
number of parts in a drive to reduce cost and improve performance.
Also, as the drives continue to increase in recording data density
and capacity, they continue to become more sensitive to particulate
and vaporous contamination, such that the existing filtration means
often do not meet these ever more demanding filtration
requirements.
Accordingly, a primary purpose of the present invention is to
provide an improved molded filter for an enclosed environment that
can filter both incoming (external) air and internal recirculating
air of particulates. A further purpose of the invention is to
provide an improved molded filter that can perform multiple
functions for filtering both incoming (external) air and internal
recirculating air of both particulates and vapor phase
contaminants.
A further purpose of the present invention is to provide a molded
multiple function part, as described above, which further
incorporates a diffusion tube.
A further purpose of the present invention is to provide a multiple
function part, as described above, which further incorporates a
gasket to help to seal the disk drive.
A further purpose of the present invention is to provide a multiple
function part, as described above, which further incorporates a
dampening material to help to reduce vibration within the disk
drive.
These and other purposes will be apparent based on the following
description.
SUMMARY OF THE INVENTION
The present invention is an improved molded filter which performs
multiple filtration functions within an enclosed environment, such
as within a computer hard disk drive. In a first embodiment, the
filter is capable of removing particulate contaminants from both
incoming (external) air and recirculating air by performing both
breather and recirculation functions when placed over a breather
hole in a disk drive. In an alternative embodiment, the filter also
incorporates an adsorbent material which allows it to remove both
particulate and vapor phase contaminants from incoming (external)
air and recirculating air within the disk drive.
The molded filter of the present invention includes a layered
construction comprising at least one protective support layer, at
least one first filter layer selected from an electret and a
triboelectret material, and at least one second filter layer, this
layered construction being molded so that it has a permanent
three-dimensional shape defining a cavity. As used herein,
"permanent" is intended to refer to a three dimensional shape that
is self-supporting and does not require any external supports to
retain the shape once formed. However, "permanent" should not be
construed to mean that it is not deformable when subjected to an
external force (e.g., crushing, or the like).
At least one substantially planar filter layer is located adjacent
to and covering the cavity in the layered construction. As used
herein, the term "substantially planar" is intended to mean that
the layer lies substantially in a single plane to conform to an
interior region of the enclosure. The substantially planar filter
layer and the layered construction are sealed together by a
suitable perimeter seal, as described in more detail herein. In an
alternative preferred embodiment, an optional adsorbent material is
contained in the cavity and is capable of filtering vapor phase
contaminants within the disk drive. In an alternative embodiment,
the filter further optionally includes a diffusion tube. Further,
depending on the requirements of the disk drive, it is also
possible to attach to the filter a gasket material for sealing the
disk drive or a dampening material to reduce vibration within the
drive.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1A is a top perspective view of one embodiment of the improved
molded multi-functional filter of the present invention.
FIG. 1B is a bottom perspective view of the filter shown in FIG.
1A.
FIG. 2A is a top view of one embodiment of the present invention
positioned in a computer disk drive assembly.
FIG. 2B is a perspective view along line x-x' of FIG. 2A.
FIG. 3 is a cross-sectional view of one embodiment of the present
invention.
FIG. 4 is a cross-sectional view of another embodiment of the
present invention incorporating a diffusion tube.
FIG. 5 is a top view of a further embodiment of the present
invention incorporating both adsorbent and a diffusion tube.
FIG. 6 shows the filter of FIG. 5 mounted over a breather hole in a
disk drive housing.
FIG. 7 is a top view of one embodiment of the present invention
wherein a gasket for sealing a disk drive is attached to the
filter.
FIG. 8 is a top view of one embodiment of the present invention
wherein a dampening material for reducing vibration in a disk drive
is attached to the filter.
FIG. 9 is a schematic of the particle capture apparatus used to
test the filters in accordance with the test descriptions contained
herein.
FIG. 10 is a schematic of the breather performance apparatus used
to test the filters in accordance with the test descriptions
contained herein.
FIG. 11 is a schematic of the vapor phase contaminant capture
apparatus used to test the filters in accordance with the test
descriptions contained herein.
FIG. 12 is a graph showing the particle capture efficiency for the
filter described in Example 1.
FIG. 13 is a graph showing the particle capture efficiency for the
filter described in Example 3.
FIG. 14 is a graph showing the particle capture efficiency for the
filter described in Example 4.
FIG. 15 is a graph showing adsorbent breather performance of the
filter described in Example 4.
FIG. 16 is a graph showing the organic material (toluene)
adsorption performance of the filter described in Example 4.
FIG. 17 is a graph showing the weight gain per unit time of the
filter described in Example 4 when subjected to a passive
adsorption test.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an improved molded filter which performs
multiple filtration functions within an enclosed environment, such
as within a computer hard disk drive. In a first embodiment, the
filter is capable of removing particulate contaminants from both
incoming (external) air and recirculating air by performing both
breather and recirculation functions when placed over a breather
hole in a disk drive. In an alternative embodiment, the filter also
incorporates an adsorbent material which allows it to remove both
particulate and vapor phase contaminants from incoming (external)
air and recirculating air within the disk drive.
Referring to FIGS. 1A and 1B, there are shown top perspective and
bottom perspective views of one embodiment of the present
invention. Particularly, the filter element 11 has a geometry which
is adapted to fit into a corner of a disk drive with a curved edge
13 which substantially mirrors the curvature of a disk within a
disk drive (not shown). The molded section 15 is attached to a
substantially planar filter layer 18 by a perimeter seal 14, the
inner edge of the seal being shown in dotted line perspective in
FIG. 1B.
FIGS. 2A and 2B show an example of the placement of a
multi-functional filter 11 of the present invention mounted in a
conventional disk drive assembly 19. As can be seen, the filter
assembly of the present invention is small enough that it can be
placed virtually anywhere in the disk drive assembly 19 and is
typically put into an area of high air flow generated from a
spinning data storage disk or disks 12, the direction of spin and
air flow indicated by the arrow. This forces air through the filter
effecting particulate filtration and gives greater access of the
adsorbent, when present, to the vapor contaminants. In addition,
when the breather hole of the disk drive assembly (not shown) is
covered by the filter, incoming air is also filtered of particulate
and/or vapor phase contaminants. Filtration occurs as the air
passes through the filtration layers which collect particulate and
as the air passes through the adsorbent, which picks up vapor phase
contaminants. The filter may be held in place by any suitable
means, preferably by an adhesive or other means which is capable of
sealing the filter around the breather hole in the disk drive
housing so that unfiltered incoming air does not leak beneath the
filter and into the drive. Another conventional element shown in
FIG. 2A is the positioning armature 17.
Referring to FIG. 3, there is shown a cross-sectional view of one
embodiment of the multi-functional filter of the present invention.
Particularly, the molded layered construction 20 includes an inner
(or second) filter layer 22 which is capable of filtering
particulates. Suitable filter layers may include filter papers or
filter membranes such as polypropylene membranes or cast polymeric
membranes or some combination of filter materials. A preferred
filter layer is expanded PTFE membrane. In a particularly preferred
embodiment, the filter layer is a layer of expanded PTFE membrane
made in accordance to U.S. Pat. No. 4,902,423 issued to Bacino et
al., specifically incorporated herein by reference. This filter
media would be structurally supported (e.g., by lamination, etc.)
by a layer of woven, non-woven or expanded porous material such as
polyester, polypropylene, polyamide, etc. This filter media has
several advantages. It can be made very highly permeable, with
resistances to air flow of less than 1.0 mm H.sub.2 O @ 10.5 feet
per minute (3.2 meters per minute). The particle filtration
efficiency of this highly expanded membrane is also very high
(e.g., in excess of 55% at 0.3 micron) which provides good particle
filtration. In addition, in cases where an adsorbent is contained
in the cavity of the filter, this filter material provides good
adsorbent containment.
Another filtration layer 24 (the "first" layer) which is part of
the molded layered construction comprises an electret or
triboelectret material which is also capable of filtering particles
in an air stream. Preferred is a layer of triboelectric material
made of PTFE and polyamide fibers such as that commercially
available from W. L. Gore and Associates, Inc. under the trademark
GORE-TRET.RTM. recirculation media. Advantages of this media are
that it is very high in efficiency (e.g., in excess of 90% @ 0.3
pm) and also very permeable (e.g., less than 1 mm H,O @ 10.5 fpm or
3.2 m/mm). While this media loses its electrostatic efficiency
while being washed with deionized water, it immediately regains its
efficiency upon drying due to the triboelectric effect of the mix
of fibers. Other electrets or triboelectret filter materials of
high efficiency and low resistance to air flow can also be
used.
An outer protective layer 26 can also be used to add durability to
the filter and to contain any protruding fibers from either the
triboelectric filter media or the filter support material for the
expanded PTFE filter media. Typically, this would be an extruded or
expanded plastic material of polypropylene, polyamide, polyester,
porous polytetrafluoroethylene, etc. Alternatively, the outer
protective layer could be a knit, woven or non-woven material. A
preferred material is a Delnet 0707 expanded polypropylene
material, available from Applied Extrusion Technologies, Inc.,
Middletown, Del.
The molded layered construction can be formed by any suitable means
which provides a permanent three-dimensional shape defining a
cavity therein. A preferred molding technique includes placing the
layers into a male and female die set and applying heat and
pressure to form the layered construction. In a preferred
embodiment, the layers are placed in a room temperature mold and
contacted with a heated male mold under only the pressure of the
weight of the male mold to form the molded construction. In a
particularly preferred embodiment, the protective layer and the
first filter layer of electret or triboelectret material is formed
in a die set as described above, then the second filter layer is
formed in a separate step in either the same die set used to form
the protective and first layers or in a second die set having
dimensions slightly smaller than the first die set so that the
molded second filter layer construction fits readily into the outer
molded construction.
Still referring to FIG. 3, a substantially planar filter layer 27
is located adjacent to and covering the cavity 28 in the molded
construction 20, and the planar filter layer 27 is sealed to the
molded construction 20 by a perimeter seal 29.
The outer perimeter seal may be a heat seal or ultrasonic seal of
the thermoplastic or thermoset layers. Alternately, a sealant, such
as an adhesive, may be used to form the outer perimeter seal, but
care should be exercised to avoid any seal material that may outgas
during manufacturing or in use. A preferred seal can be obtained
with a DuKane Model 351 Autotrace with a 40 khz rating. A weld for
0.95 second hold time at a pressure of 85 psi on the perimeter
followed by a 2.8 second hold or cooling time effects an adequate
seal with a Delnet 0707 polypropylene scrim, a GORE-TRET.RTM.
recirculation media and two layers of expanded PTFE on
polypropylene scrim (0.020 inch thick screen, 43.5 strands per
inch).
FIG. 4 shows a cross-section of an alternate filter of the present
invention which incorporates the features of FIG. 3 along with an
adhesive layer 33 incorporating a diffusion tube 30. The optional
diffusion tube may have any suitable construction which creates a
tortuous path for air entering through a breather hole in a disk
drive. A preferred diffusion tube which may be used in conjunction
with the present invention is that taught in U.S. Pat. No.
5,417,743, to Dauber, specifically incorporated herein by
reference. Alternatively, the filter may be placed over a diffusion
tube which is located in the disk drive housing, rather than on the
filter.
FIG. 5 shows a further alternative embodiment of the present
invention, in which in addition to the features shown in FIG. 4,
the filter further includes an adsorbent 32 within the cavity of
the filter.
The terms "adsorbent" and "adsorb" are not intended to be limiting
with respect to the manner or mechanism of vapor entrapment. That
is, the terms are intended to refer to materials mechanisms whereby
vapors are entrapped, whether it be adsorption, absorption or some
other mechanism. Examples of suitable adsorbent materials that may
be contained within the adsorbent layer include: physisorbers (e.g.
silica gel, activated carbon, activated alumina, molecular sieves,
etc.); chemisorbers (e.g. potassium permanganate, potassium
carbonate, potassium iodide, calcium carbonate, calcium sulfate,
sodium carbonate, sodium hydroxide, calcium hydroxide, powdered
metals or other reactants for scavenging gas phase contaminants);
ion exchange materials; catalytic fillers; as well as mixtures of
these materials.
Further, the adsorbent may comprise one or more layers of 100%
adsorbent materials, such as granular activated carbon, activated
carbon fabric or fibers, or may be a filled product matrix such as
a scaffold of porous polymeric material compounded with adsorbents
that fill the void spaces. Other possibilities include adsorbent
impregnated non-wovens or beads on a scrim where the non-woven or
scrim may be cellulose or polymeric and may include latex or other
binders as well as porous castings or tablets of adsorbents and
fillers that are polymeric or ceramic. The adsorbent may also be a
mixture of different types of adsorbents. The adsorbent may further
comprise unique geometries which present high surface area for
contact with the air in the drive, and thus enhanced adsorption,
such as those geometries described and shown in more detail
herein.
For some applications, it may be desirable to employ multiple
layers of adsorbent materials, with each layer containing different
adsorbents to selectively remove different contaminants as they
pass through the filter.
FIG. 6 shows the filter of FIG. 5 mounted over a breather hole 35
and adhered to a disk drive housing 37.
Referring to an alternative embodiment of the present invention,
FIG. 7 shows a filter element 11 of the present invention adhered
to a gasket material 40 which may be incorporated to seal the
housing components of a disk drive. Any suitable gasket material
may be used in this embodiment.
FIG. 8 shows a further alternative embodiment of the present
invention wherein the filter element 11 of the present invention is
adhered to a dampening material 44 for reducing vibration within
the disk drive housing. Any suitable dampening material may be used
in this embodiment.
Not only are the filters of the present invention simple to use and
install, but another advantage of such devices is that the filters
are not only low in outgassing and nonvolatile residues, but also
low in particulation. In addition, depending on the construction,
the filters can have the added benefit that they can be washed with
deionized water to remove surface ionic contamination and
particulation to improve their suitability for those applications
requiring cleanliness, such as in computer disk drives, without
washing out beneficial treatments such as salts which remove acid
gases from the air streams. This washability is accomplished by
using hydrophobic filter materials (along with impermeable layers
such as adhesives, etc.) to surround the adsorbent layers.
"Hydrophobic" as used in this application means the filter
materials have a water (or water with surfactant if one is used)
entry pressure sufficient to withstand the conditions of
conventional washing steps, such as heating, stirring, ultrasonics,
etc.
The present invention consolidates filtration functions which were
previously performed by two, three, or more filters into a single
filter having a novel construction that functions well, is easy to
install, is clean and cleanable. Additionally, further components,
such as a gasket or gasket(s) or vibration dampening materials, can
be included to further reduce the number of components required for
final assembly of a disk drive.
Various examples of the present invention can be described and
illustrated in the accompanying drawings and discussions.
Test Procedures
Filters formed in the examples of the present invention were tested
for adsorption and particulate filtration performance using a
commercially available 3.5 inch form factor disk drive (Model
Number 90845D4, Maxtor Corporation, Longmont, Colo.). All drive
components except the motor were removed prior to modification of
the drive for incorporation of the device. Modification consisted
of drilling a breather hole (of approximately 1/16 inch diameter)
in the baseplate allowing communication of the internal drive
environment with the external environment via the device, and
drilling two 1/4 inch diameter holes in the drive lid to allow
introduction of contaminants and sampling of the internal drive
atmosphere. Each of the holes in the lid was covered with a
stainless steel fitting, which was centered over the hole and
attached and sealed using 5 minute two-component epoxy. The
fittings were 1/4 inch NPT female to 1/8 inch Swagelok male
adapters (Part No. SS-200-7-4, Baltimore Valve and Fitting Co.,
Baltimore, Md.). The drive was cleaned using isopropanol and
pressurized air to remove any oils and particulates created during
modification. The head suspension assemblies were removed from the
E-block prior to reassembly into the drive in order to eliminate
the possibility of head crashes during testing. All components were
then reassembled into the drive prior to sealing and testing.
Recirculation Filtration Test:
This test is designed to measure the effectiveness of a
recirculation filter in reducing the particle concentration inside
a disk drive from an initial state in which the drive has been
charged with particles. The performance of the recirculation filter
is quantified in terms of a cleanup time, which is the time
required to reduce the particle counts to a fixed percentage of
their initial value.
For testing the effectiveness of the recirculation filter function
the multi-functional filter was tested in the modified disk drive
160, as schematically illustrated in FIG. 9. The existing breather
hole in the drive was left uncovered in order to provide a means
for venting 192 any overpressure from the drive and to allow air to
enter the drive during periods when the drive environment was being
sampled without air being purposefully introduced into the drive.
The lid was fastened securely to the base plate. A tube supplying
an aerosol mixture of 0.1 .mu.m and 0.3 .mu.m particles was
connected to the port in the drive lid which was upstream 194 of
the filter based on the direction of disk rotation. A second tube
for sampling the internal atmosphere of the drive connected the
laser particle counter 166 (LPC) to the port 164 in the drive lid
which was downstream of the filter. Sample flow rate out of the
drive and through the counter 166 was maintained at 1 cc/sec and
sheath flow through the LPC 166 was maintained at 40 cc/sec. Counts
of 0.1 .mu.m and 0.3 .mu.m particles were obtained once per second
by the LPC 166 and stored on a computer 172 disk drive for later
analysis. The test was performed with the drive 160 located in a
laminar flow hood fitted with a HEPA filter in the air intake, in
order to maintain a controlled test environment with an extremely
low ambient particle concentration. A control drive of the same
model and also having had its head suspension assemblies removed
and containing no recirculation filter was tested.
The recirculation filter test consisted of the following sequence:
With the drive 160 powered on and clean air passing through the
drive, the counts of 0.1 .mu.m and 0.3 .mu.m particles were
monitored until a low background count was achieved, typically when
0.3 .mu.m particles were less than 3 counts per second and 0.1
.mu.m particles were less than 10 counts per second. At that point
in time, the aerosol was flowed into the drive 160 in order to
charge the internal environment with particles. When fully charged
and stabilized, counts of 0.1 .mu.m particles were typically
between 10000 and 20000 per second and counts of 0.3 .mu.m
particles were typically between 3000 and 6500 per second. The flow
of aerosol into the drive 160 was then halted while sampling of the
internal drive atmosphere continued, by drawing out of the drive
air which entered through the open breather hole in the base plate
as well as any leaks in the lid or base plate. The concentration of
0.1 .mu.m and 0.3 .mu.m particles was observed to drop over time
due to the recirculation of air through the drive and the filter,
impaction of the particles on surfaces inside the drive, and the
gradual exchange of particle-laden air with clean air drawn in
through the breather hole. Monitoring of the drive 160 continued
until the particle counts dropped to the initial background values
observed prior to charging the drive with aerosol. The
concentration of 0.1 .mu.m and 0.3 .mu.m particles was observed to
drop over time due to the recirculation of air through the drive
and the filter, impaction of the particles on surfaces inside the
drive, and the gradual exchange of particle-laden air with clean
air drawn in through the breather hole.
Breather Filtration Test:
This test is designed to measure the effectiveness of a breather
filter in reducing the particle concentration inside a disk drive
when the drive is placed in an environment heavily laden with fine
particles and air is forcibly drawn into the drive. The performance
of the breather filter is quantified by an efficiency, which is the
percentage reduction in particle concentration between the external
and internal environments of the drive.
The filter of the Example was tested in the modified disk drive,
and the pre-existing breather hole in the drive was covered with
metallized tape. The lid was fastened securely to the base plate
and tape was applied over the screw holes in the lid as well as
along the periphery of the drive to seal off any extraneous leaks.
A control drive, of the same model and also having had its head
suspension assemblies removed, contained no breather filter. The
pre-existing breather hole in the base plate was left uncovered in
the control drive to simulate an imperfectly sealed drive.
As schematically illustrated in FIG. 10, the disk drive 160 was
placed inside a stainless steel box 162. One of the two ports in
the lid (that which was upstream of the filter based on the
direction of disk rotation) was capped to prevent air flow through
the fitting. The downstream port 164 was connected using a 1/8 inch
outside diameter flexible tube to a port in the wall of the metal
box 162, which was connected on the outside of the box via tubing
to a laser particle counter (LPC) 166 (Model LAS-X, Particle
Measuring Systems, Inc., Boulder, Colo.). Sample flow rate out of
the drive 160 and through the LPC 166 was maintained using a flow
meter and valve 168 at 1 cc/sec and sheath flow through the LPC 166
was maintained at 40 cc/sec. A second port in the wall of the metal
box 162 was connected to a 6 inch length of 1/4 inch inner diameter
flexible tubing opening onto the interior of the box. The line for
sampling the atmosphere in the box was also connected to the LPC
166. The two lines running from the box to the LPC were each
connected to a length of flexible tubing passing through a valve
170 which was electronically controlled by computer 172 to
simultaneously close off one line while opening the second. Upon
exiting the selector valve 170 the two lines met in a `Y` junction,
allowing the LPC 166 to sample one line at a time. A third port in
the wall of the metal box 162 was used for the introduction of an
aerosol into the internal environment of the box. The aerosol
stream passed through a fitting in the port and then was divided
into two streams, each of which flowed through a separate tube and
entered the box through three gas dispersion tubes (Part Number
P-06614-25, Cole-Parmer Instrument Company, Vernon Hills, Ill.).
The aerosol consisted of an aqueous suspension of 0.1 .mu.m and 0.3
.mu.m diameter polystyrene latex (PSL) spheres (Catalog Number
5010A and 5030A, Duke Scientific Corporation, Palo Alto, Calif.)
which provided an approximately 5:1 ratio of 0.1 .mu.m to 0.3 .mu.m
particles as sampled from the metal box 162. The aerosol was
generated by passing filtered compressed air 174 at a regulated
(regulator 176) pressure of 39 psi (2.7.times.105 Pa) through an
atomizer 178 containing the suspension, and further mixing this
with a stream of air 180 regulated to 2 psi (1.38.times.104 Pa).
The aerosol was subsequently passed through a drying tube 182 to
evaporate water from the droplets, creating a stream composed
primarily of discrete particles. Flow of the dried aerosol stream
was controlled by a manual valve 184, allowing a portion of the
stream to vent to atmosphere 186 and then through an electrical
on/off valve 188 controlled by computer 172. Electrical power 190
to the drive was provided by an electrical connection through a
fourth port through the wall of the metal box 162 which was not
sealed tightly in order to provide a means for venting to
atmosphere 192 any overpressure from the box 162.
After the drive 160 was placed in the box 162 and the connections
made for power and air sampling, a gasketed lid was clamped
securely to the top of the box 162. Breather tests were performed
with both the drive motor off and on. In the case of tests where
the motor was on, proper motor function was tested prior to sealing
the box 162, and then verified during testing by measuring the
current through the electrical power wires using a current
probe.
The breather filter test was performed as follows: The aerosol flow
was turned on at the beginning of the test and remained on
throughout the duration of the test. Initially, the box was charged
with particles for 120 seconds. Then the box was sampled for 180
seconds in order to allow the particle counts to stabilize, and
during which time no data was recorded. Subsequently, the number of
0.1 .mu.m and 0.3 .mu.m particles from the box were counted and
recorded every 5 seconds for 100 seconds. Next, the drive was
allowed to settle for 180 seconds and then sampled every 5 seconds
for 100 seconds. The box and drive were monitored for two
additional cycles in this same manner, each time allowing 180
seconds for stabilization of the counts and 100 seconds of sampling
for both box and drive. Typical levels of the aerosol particles as
sampled from the metal box were between 11500 and 18000 per 5
second interval for 0.1 .mu.m particles and between 2200 and 3700
per 5 second interval for 0.3 .mu.m particles.
The data recordings were analyzed by obtaining the average particle
counts for the box and the drive for each of the three cycles. The
efficiency for each cycle was calculated using the following
formula:
The three efficiency values were then averaged together to obtain
the overall breather filter efficiency. This analysis was performed
separately for 0.1 .mu.m and 0.3 .mu.m particles.
Disk Drive Adsorption Test:
This test is designed to measure the effectiveness of a
multi-functional filter in reducing the concentration of a volatile
organic contaminant, toluene, inside a disk drive relative to the
concentration of toluene in an inlet stream flowing into the drive.
The performance of the multi-functional filter is quantified by
calculating the percentage of the inlet concentration of toluene
detected in the drive vapor space.
The device was tested in the modified disk drive 160, as shown in
FIG. 12. In addition to the two ports made in the drive lid, a 1/16
inch outside diameter rigid TEFLON.RTM. tube (obtained from
Cole-Parmer Instrument Company, Vernon Hills, Ill.) was inserted
from the outside through the bottom of the base plate into the
breather hole, to create a third port. The penetration of this tube
into the breather hole was limited in such a manner that the end of
the tube remained below the internal surface of the base plate. An
airtight seal was created around the external juncture between the
tube and the base plate using two-component epoxy. Following these
further modifications of the drive 160, the filter of the Example
was mounted into the base plate as earlier described, such that the
hole in the bottom adhesive was located over the breather hole
specially made for testing the device. The pre-existing breather
hole in the drive was covered with metallized tape. The remaining
components were then reassembled into the drive. The drive was
resealed, and adhesive tape was used to seal all potential paths
for significant air leaks. A control drive of the same model which
contained no adsorbent was also tested.
The drive motor was continuously spinning during all testing. The
disk drive 160 was purged with clean dry air to verify that initial
toluene concentration was 0 ppm. One of the three ports into the
drive was capped off. Clean dry air 196 was passed through a
pressure regulator 198 and mass flow controller 200 to generate an
air stream at a constant volumetric flow rate of 40 ml/min, flowing
into one of the two other ports on the drive 160. The remaining
port was connected to a flow meter to monitor for any flow loss.
The outlet flow into the flow meter was measured to be at least 95%
of the inlet stream, and thus the drive was considered adequately
sealed for testing.
For testing adsorbent breather functionality of the
multi-functional filter, 100 ppm toluene in nitrogen 202 was passed
through a pressure regulator 204 and mass flow controller 206, and
mixed with clean dry air to generate a room temperature stream of
25 ppm toluene in air. This toluene stream was flowed directly into
the part, through the tube adhered to the breather hole, at a
volumetric flow rate of 40 ml/min. One of the two ports in the lid
was closed with a cap. Rigid TEFLON.RTM. tubing was used to connect
the second port in the lid via a sampling valve 208 to a gas
chromatograph equipped with a flame ionization detector (FID) 210
to monitor toluene concentration inside the drive. The data
recordings were collected on a personal computer 212 and analyzed
by calculating a percentage from the ratio of the sampled
concentration and a nominal inlet concentration of 25 ppm over the
duration of the test. For testing the adsorbent recirculation
functionality of the filter, a cap was used to seal the tube
entering the breather hole over which the device was situated. The
pre-existing breather hole in the drive 160 remained sealed with
metallized tape. A room temperature stream of 25 ppm toluene in
clean dry air was then flowed into the drive 160 through the port
in the lid which was upstream of the test sample, at a volumetric
flow rate of 40 ml/min. The second port in the lid was connected to
the FID 210 with rigid TEFLON.RTM. tubing, in order to monitor
toluene concentration inside the drive. The data were analyzed by
calculating a percentage from the ratio of the sampled
concentration and a nominal inlet concentration of 25 ppm over the
duration of the test.
Passive Disk Drive Adsorption Test
This test is designed to measure the initial adsorption uptake of a
volatile organic contaminant, toluene, by an adsorbent filter under
static conditions, i.e., adsorption under constant gas/vapor
concentration without significant convective gas flow. The
performance of the adsorbent filter is quantified in terms of an
adsorption rate, which is the average weight increase of the
adsorbent filter per unit time.
For measuring the passive adsorption uptake, the rigid
multi-functional filter of the Example was adhered to a small sheet
of plastic which covered the entire bottom surface, such that the
entrance to the diffusion tube was completely sealed off. A small
hole had been punched in a portion of the plastic sheet protruding
out from under the filter, which was used to suspend the filter
from a hook attached to the microbalance. The glass sample chamber
was sealed around the sample. Water from a constant temperature
bath was circulated through a jacket surrounding the sample chamber
until the system reached a steady temperature of 25.degree. C. The
chamber was then flushed with clean dry air until the microbalance
recorded a constant weight, signifying the elimination of moisture
from the sample.
To start the vapor adsorption process, the microbalance was tared,
and a mixture of toluene and air was passed through a flow
controller and allowed to flow into the chamber from below and out
through a vent at the top. The toluene stream had a flow rate of 1
liter/min and a concentration of 25 ppm by volume. Based on this
volumetric flow rate and the cross-sectional area of the sample
chamber, the linear flow velocity was calculated to be around 0.9
mm/second. This linear flow velocity was chosen based on the
assumption that it would be sufficiently low to prevent convective
flow through the device, which may possibly have an impact on the
adsorption rate. The weight of the device was monitored for several
hours and recorded using a computer-based data acquisition system.
The data recordings were analyzed by performing a linear regression
through the weight data for the device vs. time. The resulting
slope provides a measure of the passive adsorption rate through the
openings in the filter, which would be in direct fluid
communication with the interior of a disk drive.
Particle Removal Test
A Maxtor Diamond Max Model number 9084504 disk drive was purchased.
The disk drive was opened and the heads removed. In addition, the
post in the corner to support the existing recirculation filter was
removed. The filters tested were each adhered to the base casting
in the same location as the previously existing recirculation
filter.
The disk drive was then resealed. The disk drive was purged and
then challenged with a flow of 0.3 and 0.1 micron particles. The
number of particles in the disk drive was allowed to come to
equilibrium and then the flow of particles was stopped. The rate of
decay of particles in the drive air space was recorded as the
filter collected the particles. In this test the more efficient the
filter, the lower the time to get to 99.9% removal.
EXAMPLES
Example 1
A filter of the present invention having a generally rounded
triangular geometry to fit into a corner of a disk drive and with
general dimensions of 2.0 cm by 1.7 cm by 3.0 cm was manufactured
as described below.
Three layers consisting of, respectively, a Delnet 0707
polypropylene scrim (Applied Extrusion Technologies, Inc.,
Middletown, Del.), a Reemay B2004 non-woven polyester (Reemay,
Inc., Old Hickory, Tenn.), and an electrostatic felt material
consisting of GORE-TRET.RTM. recirculation media (available from W.
L. Gore and Associates, Inc., Elkton, Md.) were placed over a
female die having the general dimensions of 2.0 cm by 1.7 cm by 3.0
cm so that the scrim material faced the female die. The 3.0 cm
dimension was shaped to mirror the die with a radius of curvature
of 4.9 cm. The general shape of the part is a right triangle with a
radius of curvature of 0.8 cm replacing the 90 degree angle. The
female die had 6 vacuum holes located with the die set and was at
room temperature. The layers were placed over the female die, the
female die was placed inside an ultrasonic sealer and the vacuum
was turned on and pulled through the 6 vacuum holes. A male die
made 0.2 mm smaller than each of the overall dimensions of the
female die was heated to 340.degree. F. The female and male die set
was placed in a Model Phase II Arbor Press. The male die was then
gently pressed into the female die. No additional pressure except
the weight of the die was used. By this step, a form was made from
the layered sheets having the shape of the mold and having a cavity
therein.
A two layer laminate of polypropylene/ePTFE membrane was then
placed on top of the molded form so that it covered the cavity to
form a substantially planar filter layer lid. The laminate was
formed using an ePTFE membrane having an 0.2 micron average pore
size, a thickness of 0.0027-0.0039 inches and a Gurley number that
ranged from 10-18 sec. The polypropylene was a 0.020 inch thick
screen with biaxially oriented fibers at an 80 degree angle to each
other. The strand count was an average of 43.5 strands/inch. The
lamination was carried out by heat and pressure at conditions of
220.degree. C. and 50 psia. The polypropylene side of the laminate
was oriented toward the molded part containing the adsorbent.
The two layer laminate was bonded to the molded part in the
following manner. The ultrasonic sealer was a DuKane model 351
Autotrace with a 40 khz rating. The following settings were used on
the ultrasonic equipment: The dial was set to maximum power with an
85 psi seal pressure. The trigger pressure setting was 1.45. The
hold time was 2.8 seconds with a weld time of 0.95 sec.
An adhesive layer of double-sided adhesive tape comprising two
layers 0.001" thick (0.025 mm) of permanent high temperature, low
outgassing, acrylic pressure sensitive adhesive on both sides of a
two mil polyester film carrier was placed on the outer surface of
the substantially planar filter layer to secure the filter to a
disk drive during testing. The resulting filter was tested in the
manner described herein.
Example 2
A self adhesive adsorbent filter having the features generally
shown in FIG. 1 was formed, in which one side of the filter was
shaped to mirror the curvature of the disk. The filter was
manufactured using the following process and materials.
Three layers of material, as described in Example 1, were placed
over a female die having the general dimensions of 2.0 cm by 1.7 cm
by 3.0 cm so that the scrim material faced the female die. The 3.0
cm dimension was shaped to mirror the die with a radius of
curvature of 4.9 cm. The general shape of the part is a right
triangle with a radius of curvature of 0.8 cm replacing the 90
degree angle. The female die had 6 vacuum holes located with the
die set and was at room temperature. The layers were placed over
the female die, the female die was placed inside an ultrasonic
sealer and the vacuum was turned on and pulled through the 6 vacuum
holes. A male die made 0.2 mm smaller than each of the overall
dimensions of the female die was heated to 340.degree. F. The
female and male die set was placed in a Model Phase II Arbor Press.
The male die was then gently pressed into the female die. No
additional pressure except the weight of the die was used. By this
step, a form was made from the layered sheets having the shape of
the mold and having a cavity therein.
A second molded component was formed from a laminate of expanded
PTFE and polypropylene backer. The laminate was formed from a
membrane having an 0.2 micron average pore size, a thickness of
0.0027-0.0039 inches and a Gurley number that ranged from 10-18
sec. The polypropylene was a 0.020 inch thick screen with biaxially
oriented fibers at an 80 degree angle to each other. The strand
count was an average of 43.5 strands/inch. The lamination was
carried out by heat and pressure at conditions of 220.degree. C.
and 50 psia. A female mold having a shape substantially the same as
the first female mold mentioned above, except that the mold had
dimensions of 1.850 cm by 1.550 cm by 2.850 cm, was obtained having
six vacuum holes therein. The laminate was placed over the female
die, the female die was placed inside an ultrasonic sealer and the
vacuum was turned on and pulled through the 6 vacuum holes. The
female mold was at room temperature during this procedure. A male
die having dimensions which were 0.2 mm smaller than the dimensions
of the female die was heated to 340.degree. F. and placed into the
female die so that the laminate was held between the die set. The
die set was placed in the Arbor Press described above and the male
die was gently pressed into the female die. No additional pressure
except the weight of the die was used. By this step, a second form
was made from the layered sheets having the shape of the mold and
having a cavity therein.
The second form was then placed inside the first form which was
still in the first female die, and the assembly was placed in the
ultrasonic sealer. The vacuum was turned on, and an adsorbent
comprising 500 mg of loose activated carbon was then placed in the
cavity of the second form. The activated carbon had an average
diameter of 0.6 mm, a 1200 m.sup.2 /gram specific surface area, and
0.57 cc/gram pore volume.
A two layer laminate of the same polypropylene/ePTFE membrane used
to make the second form was then placed on top of the molded forms
so that it covered the adsorbent fill to form a lid comprising a
substantially planar filter layer. The polypropylene side of the
laminate was oriented toward the molded part containing the
adsorbent.
The substantially planar two layer laminate was bonded to the
molded part containing the adsorbent in the following manner. The
ultrasonic sealer was a DuKane Model 351 Autotrace with a 40 khz
rating. The following settings were used on the ultrasonic
equipment: The dial was set to maximum power with an 85 psi seal
pressure. The trigger pressure setting was 1.45. The hold time was
2.8 seconds with a weld time of 0.95 sec.
An adhesive layer comprising two layers 0.001" thick (0.025 mm) of
permanent high temperature, low outgassing, acrylic pressure
sensitive adhesive on both sides of a two mil polyester film
carrier was placed on the outer surface of the substantially planar
filter layer to secure the filter to a disk drive during testing.
The resulting filter was tested in the manner described herein.
Example 3
A filter was made as described in Example 2. Onto the substantially
planar filter lid of the filter was adhered a diffusion tube made
with a layer of double-sided adhesive tape comprising two layers
0.001" thick (0.025 mm) of permanent high temperature, low
outgassing, acrylic pressure sensitive adhesive on both sides of a
two mil polyester film carrier. The diffusion tube hole was cut
into this layer and configured to mate one end to the hole through
the drive base plate. This hole, along with a majority of the
diffusion tube length, was covered with a single sided adhesive
tape comprising a layer of 0.001" (0.025 mm) thick permanent high
temperature, low outgassing, acrylic pressure sensitive adhesive on
a 0.002" (0.051 mm) thick polyester carrier. The other end of the
diffusion tube was left uncovered to allow airflow through the
filter layers and into the drive. An exposed adhesive layer on the
diffusion tube was used to secure the filter to a disk drive during
testing. The resulting filter was tested in the manner described
herein.
Example 4
A filter as shown generally in FIG. 6 was formed having a shape on
one side to mirror the curvature of the disk. The filter was
manufactured using the process and materials described below.
A laminate of expanded PTFE and polypropylene backer was formed.
The laminate was formed from a the membrane having an 0.2 micron
average pore size, a thickness of 0.0027-0.0039 inches and a Gurley
number that ranged from 10-18 sec. The polypropylene was a 0.020
inch thick screen with biaxially oriented fibers at an 80 degree
angle to each other. The strand count was an average of 43.5
strands/inch. The lamination was carried out by heat and pressure
at conditions of 220.degree. C. and 50 psia.
The laminate was placed over a female die having the general
dimensions of 2.0 cm by 1.7 cm by 3.0 cm so that the scrim material
faced the female die. The 3.0 cm dimension was shaped to mirror the
die with a radius of curvature of 4.9 cm. The general shape of the
part is a right triangle with a radius of curvature of 0.8 cm
replacing the 90 degree angle. The female die had 6 vacuum holes
located with the die set and was at room temperature. The layers
were placed over the female die, the female die was placed inside
an ultrasonic sealer and the vacuum was turned on and pulled
through the 6 vacuum holes. A male die made 0.2 mm smaller than
each of the overall dimensions of the female die was heated to
340.degree. F. The female and male die set was placed in a Model
Phase II Arbor Press. The male die was then gently pressed into the
female die. No additional pressure except the weight of the die was
used. By this step, a form was made from the layered sheets having
the shape of the mold and having a cavity therein.
A three layer construction was then laid over the same female die
set described above. The three layers, consisting of, respectively,
a Delnet 0707 polypropylene scrim (Applied Extrusion Technologies,
Inc., Middletown, Del.), a Reemay B2004 non-woven polyester
(Reemay, Inc., Old Hickory, Tenn.), and an electrostatic felt
material consisting of GORE-TRET.RTM. recirculation media
(available from W. L. Gore and Associates, Inc., Elkton, Md.) were
placed over the female die so that the scrim material faced the
female die. The same steps as described above were used to mold the
three layers into the shape of the die set.
The ePTFE laminate made in the first step was placed inside the
molded tri-layer construction. The two forms were then placed
inside the female die form inside a ultrasonic sealer, and the
vacuum was turned on. An adsorbent comprising 500 mg of silica gel
and 200 mg of treated activated carbon was placed inside the molded
cavity.
A layer of the same laminate of polypropylene/ePTFE used in the
first step of the example was placed on top of the molded part so
that it covered the adsorbent fill with the polypropylene layer
toward the molded part to form a substantially planar filter lid.
The lid was then sealed onto the part with an ultrasonic sealer to
complete the assembly. Specifically, the ultrasonic sealer was a
DuKane model 351 Autotrace with a 40 khz rating. The following
settings were used on the ultrasonic equipment. The dial was set to
Max power with an 85 psi seal pressure. The trigger pressure
setting was 1.45. The hold time was 2.8 seconds with a weld time of
0.95 sec.
Onto the substantially planar filter lid of the filter was adhered
a diffusion tube made with a layer of double-sided adhesive tape
comprising two layers 0.001" thick (0.025 mm) of permanent high
temperature, low outgassing, acrylic pressure sensitive adhesive on
both sides of a two mil polyester film carrier. The diffusion tube
hole was cut into this layer and configured to mate one end to the
hole through the drive base plate. This hole, along with a majority
of the diffusion tube length, was covered with a single sided
adhesive tape comprising a layer of 0.001" (0.025 mm) thick
permanent high temperature, low outgassing, acrylic pressure
sensitive adhesive on a 0.002" (0.051 mm) thick polyester carrier.
The other end of the diffusion tube was left uncovered to allow
airflow through the filter layers and into the drive. An exposed
adhesive layer on the diffusion tube was used to secure the filter
to a disk drive during testing. The resulting filter was tested in
the manner described herein.
A number of the filters made in the Examples above were subjected
to the Particle Removal test described earlier herein. The results
are shown below.
seconds to 99.9% particle removal (0.3 micron) Run Filter 1 2 3
Average No filter 203 198 200 200 Filter - Example 1 38 40 40 39
Filter - Example 2 52 53 56 54 Filter - Example 4 77 72 75 75
FIG. 12 is a graph depicting the time (in seconds) required to
remove 0.3 micron particles from the disk drive with no
recirculation filter (darker line) and with the filter described in
Example 1 (lighter line).
FIG. 13 is a graph depicting the time (in seconds) required to
remove 0.3 micron particles from the disk drive with no
recirculation filter(darker line) and with the filter described in
Example 3 (lighter line). FIG. 14 is a graph depicting the time (in
seconds) required to remove 0.3 micron particles from the disk
drive with no recirculation filter(darker line) and with the filter
described in Example 4 (lighter line).
The breather filter functionality of the filters made in the
Example 4 was tested using the procedure described earlier herein.
Testing was performed both with the drive running (both breather
filter and recirculation filter functioning), as well as with the
drive not running when mostly the breather filter alone was
functioning. The following results in Table 2 were obtained for
three repetitive runs at each condition with the averages and %
cleanup efficiencies calculated:
TABLE 2 (0.1 micron particles) (0.3 micron particles) Percent
efficiency Percent efficiency Run number of filter Run number of
filter Motor on Run 1 99.93 Run 1 99.95 Run 2 99.95 Run 2 99.95 Run
3 99.95 Run 3 99.95 Average 99.94 Average 99.95 Motor off Run 1
99.86 Run 1 99.85 Run 2 99.87 Run 2 99.90 Run 3 99.87 Run 3 99.90
Average 99.87 Average 99.88
This illustrates the breather filter functions well and the
combination recirculation filter and breather filter (drive on
condition) performs better than either filter alone.
The adsorption breather functionality of the filter of Example 4
was then tested as previously described by forcing air with 25 ppm
of toluene through the filter described in Example 4, a standard
non-adsorbent breather and an adsorbent breather filter for
comparison. The result is shown in FIG. 15 plotting the current
invention versus a standard particulate non-adsorbent breather
filter, illustrating that the filter of the current invention
performs as an adsorbent breather is expected to function to adsorb
the toluene.
The organic adsorption functionality of the filter made in Example
4 for adsorbing contaminants in the recirculating air around the
filter was then tested as previously described by loading the drive
with a steady stream of toluene laden air and sampling the drive
when running with and without the filter. The result is shown in
FIG. 16 illustrating that the filter is capable of adsorbing the
toluene in the recirculating air and keeping the drive about 90%
cleaner compared to a drive in which no filter was present.
The filter of Example 4 was further tested in a passive adsorption
test as previously described. The weight gain per unit time is
shown in FIG. 17 illustrating that the filter works in a passive
mode and will adsorb contaminants outgassing from the internal
drive components in a passive or at-rest (non-operating) state.
While particular embodiments of the present invention have been
illustrated and described herein, the present invention should not
be limited to such illustrations and descriptions. It should be
apparent that changes and modifications may be incorporated and
embodied as part of the present invention within the scope of the
following claims.
* * * * *